Method of destroying undesirable vegetation



3,012,872 METHOI) 8F DESTROYING UNDESIRABLE VEGETATION Sidney B. Richter, Chicago, 111., assignor to Velsicol Chemical Corporation, Chicago, BL, a corporation of Illinois No Drawing. Filed Oct. 13, 1958, Ser. No. 766,661 10 Claims. (Cl. 712.6)

This invention relates to new herbicidal compositions of matter. More specifically, this invention relates to the control of undesirable plant life with 2,6-dimethoxy-3- chlorobenzoic acid, its anhydride, its amides, its esters, its alkali metal salts, or its amine salts. 2,6-dimethoxy-3- chlorobenzoic acid, which has the structure (IJOOH HaCO O CH:

will hereinafter be referred to as compound I. This chemical compound and its derivatives as cited above have marked activity as herbicides useful for the control of undesirable plant life.

Compound I can be prepared readily, for example, from the known compound 2,6-dihydroxyacetophenone. An alkali metal salt of the dihydroxy compound is methylated in aqueous solution with an excess of dimethyl sulfate. The resulting 2,6-dimethoxyacetophenone is then treated with alkaline sodium hypochlorite solution. This reaction simultaneously effects oxidation of the ketone to the carboxylic acid and introduction of a chlorine atom into the molecule to give the desired compound I. The product is isolated by acidification of the reaction mixture, as with hydrochloric acid. The compound I obtained in this manner is suitable for many herbicidal uses as such, but if desired, it can be purified by crystallization from a suitable solvent such as benzene. Alternately, compound I can be prepared by the direct chlorination of 2,6-dimethoxybenzoic acid.

The anhydride of compound I is prepared by the removal of one molecule of water from two molecules of compound I as the free acid. In practice, it is convenient to prepare the anhydride by the acylation of the free carboxylic acid by its acid halide in the presence of a strong acylating agent such as pyridine. Thus a mixture of dry pyridine and dry benzene are treated with 1 mole of the acid chloride of compound I. The slightly exothermic reaction proceeds with the formation of an in termediate pyridinium salt. One mole of compound I as the free acid is then added, the precipitate of pyridine hydrochloride is removed, and the anhydride of compound I is isolated by removal of the benzene.

The acid halide of compound I required in the above and other syntheses is prepared by the reaction of the free acid with a phosphorus trihalide in the conventional manner. Thus the treatment of compound I withphosphorus trichloride until the reaction ceases produces the acid chloride of compound I. 7

Compounds which are salts, esters, or amides of compound I can be prepared readily from the free acid. Thus treatment of the free acid with ammonium hydroxide gives a product which is the salt ammonium 2,6-dimethoxy-3- chlorobenzoate. Similarly, an alkali metal salt of compound I can be made by the treatment of the free acid with bases, such as the hydroxides, of alkali metals. Treatment of the acid with sodium hydroxide thus gives the salt sodium 2,6-dimethoxy-3-chlorobenzoate as the product, while the use of potassium hydroxide gives the salt potassium 2,6-dimethoxy-3-chlorobenzoate.

" 'at'ent Amine salts of compound I are prepared by the addi tion of the free acid to various amines. Typical amines which can be used to prepare such amine salts are dimethylamine, trimethylamine, triethylamine, diethanolamine, triethanolamine, isopropylamine, morpholine, and

- the like. The resulting products are, respectively, the

dimethylamine, trimethylamine, triethylarnine, diethanol-' I like are useful products in accordance with this invention,

of the-free amine which remains.

preferred esters are those in which the esterifying group is an unsubstituted alkyl group which contains from 1 to 10 carbon atoms. The condensation of the acid with the alcohol is carried out suitably in an inert solvent such as an aromatic hydrocarbon and in the presence of a few percent by' weight of an acid catalyst such as p-toluenesulfonic acid. The Water which forms during the esterification reaction can be removedcontinuously in many cases from the reaction mixture by distillation as it forms, and its volume can be measured to determine when the esterification is complete. The ester is then isolated by distillation of the inert solvent.

Amides of compound I can be prepared conveniently by the reaction of the acid halides of compound I with ammoniaor various amines. The reaction can be carried out in an inert solvent such as ether or' benzene. Preferably'two moles of the amine are used for each mole of the acid halide employed, since the hydrogen halide released during the reaction is taken up by some V 2,6-dimethoxy 3-chlorobenzamide, can be prepared by the reaction of the acid chlorideof compound I with ammonia, either as the free gas or as an aqueous solution. This amide can also'beprepared by hydrolysis of the corresponding nitrile. Substituted amides are prepared by the reaction of the acid halide of compound I with amines such as any ofthe primary or secondary amines suggested above for'the preparation of the amine salts of compound I. Thus, for example, the reaction of the 7 acid chloride of compound I with methylamine, butylamine, decylamine, or diethylamine gives the N-methyl, N-buty1-, N-decyl-, or N,N-diethyl-2,6-dimethoxy-3-chlorobenzamides,respectively. While more complex amines such as the aromatic .aminescan be used as the amine reactant to give desirable products, which are specifically named as anilide's, preferred amine reactants are alkylamines containing up to 10 carbon atoms.

For practical use as'herbicides, the compounds of this invention are formulated with inert carriers to obtain proper'concentrations and to facilitate handling. For example, these compounds can be formulated into dusts by combining them with such inert substances as talc or clays. The alkali metal salts of compound I are particularly suited to such dust formulations, and dusts containing from 5 to 25 percent by Weight of active compound are convenient for use in the field. The compounds of I, which ordinarily are liquids at this invention, however, are preferably applied as'sprays. These can be made as simple solutions by dissolving the compounds in organic solventssuch as xylene, kerosene, or the methylated naphthalenes. The esters of compound room temperature, are

Thus the con- The simplest amide,

3 particularly suited to formulation by this method. The amine salts of compound I often show good solubility in water and can be used directly as aqueous solutions.

The compounds of this invention can also be emulsified or suspended in water by the addition of emulsifiers and wetting agents. The formulations of these active herbicidal compounds are either applied directly to the plants to be controlled, or the soil in which the plants are growing can be treated. Substances such as other pesticides, stabilizers, activators, synergists, spreaders and adhesives can be added to the formulations if desired. There is no significant ditference in effect from the amount of water or organic solvent for diluting these herbicides, providing the same amount of chemical is distributed evenly over a given area. Such distribution can be obtained, for example, with low-pressure, lowvolume sprays at the rate of about gallons of spray per acre. I

In applying the herbicidal compounds, consideration must be given to the nature and stage of growth of the crop, the species of weeds present, the stage of growth of the weeds, environmental factors influencing the rate and vigor of the weed growth, weather conditions at the time of application and immediately following, and the dosage to be applied to a given area. Weeds are most susceptible when they are small and growing rapidly. Early application, therefore, results in better control with less chemical and increased yields because of the early destruction of the competing weeds. The larger and older the weeds the higher the concentration needed to kill them. Summer annuals such as lam-bs-quarters, pigweeds, cocklebur, and sunflower should be sprayed when they are less than 4 inches high. Winter annuals such as various mustards, fan-weed, yellow star-thistle, and wild radish are most easily killed while they are still in the rosette stage. Usually weeds growing rapidly under optimum conditions are relatively susceptible, whereas those growing under adverse conditions tend to be resistant to the herbicide sprays.

The effectiveness of the compounds of this invention in small quantities makes them economically sound for weed control on large areas, with a great saving in labor and cost, in addition to corresponding crop increases. These compounds are particularly valuable in weed control because they are harmful to many weeds but harmless or relatively harmless to some cultivated crops. Mi-

nute quantities in contact with plant tissues may be absorbed and translocated to all parts of the plant, causing striking changes in the form and functions and often resulting in their death. The actual amount of compound to be used depends on a variety of factors but is influenced primarily by the species of undesirable plant to be controlled. Thus while fractions of a pound of actual compound I or its equivalent of an ester, salt, amide, or the anhydride of compound I are often sufiicient for postemergence weed control on an acre of corn, seed flax, perennial grass seed crops, pastures or grazing areas (without legumes), wheat, and the like, the particular species of weeds encountered in evergreen and deciduous dormant nursely stock, nursery conifers, waste areas, woody brush, and the like may requirethe use of one or more pounds of compound I or its derivatives per acre for good control. Dosage adjustments with the lowvolume, low-pressure applications suggested can be made by changing the nozzle size, nozzle spacing, pressure, or traveling rate of the spray equipment.

The manner in which the herbicidal compounds of this invention can be prepared and utilized is illustrated in the following examples:

EXAMPLE 1 Preparation of 2,6 dimethoxyacelophenone cc; of water of 133 g. of 2,6-dihydroxyacetophenone (prepared as described by Russell and Frye, Organic Syntheses, vol. 21, p. 22) in a l-liter, round-bottomed flask fitted with a reflux condenser, mechanical stirrer, and dropping funnel. Dimethyl sulfate (320 g.) is then added with stirring at a rate suflicient to maintain gentle ebullition, and the mixture is stirred and heated on the steam bath for 30 minutes. More dimethyl sulfate (50 g.) is added, after which the mixture is made alkaline with 2 N sodium hydroxide. The mixture is cooled, and the product is filtered and washed with cold water. The dried product is distilled in vacuo to give 127 g. of 2,6- dimethoxyacetophenone, B.P. 1l8-20/1.5 mm., M.P. 65-6.

EXAMPLE 2 Preparation of 2,6-dimethoxy-3-chlorobenzoic acid (compound I) A solution of sodium hydroxide (110 g.) in 100 cc. of water is added to 1 kilo of cracked ice in. a 2-liter, round-bottomed flask fitted with a mechanical stirrer, reflux condenser, and gas inlet tube. Chlorine gas (89 g.) is passed into the mixture to give a solution which is neutral to litmus. Anadditional 50 g. of sodium hydroxide in 200 cc. of water is added. 2,6-dirnethoxyacetophenone (60 g.) is added dropwise with stirring to this solution at 65 C. over a period of 0.5 hour, after which the mixture is stirred at for 1.5 hours. The mixture is then cooled and acidified to Congo red with hydrochloric acid. The product is filtered off, washed with cold water, and crystallized from benzene to give 2,6-dimethoxy-3-chlorobenzoic acid, M.P. 132.

EXAMPLE 3 Preparation of the sodium salt of compound I Preparation of the ammonium salt of compound 1 Treatment of compound I (0.5 mole) in 500 cc. of methanol with 34 cc. of commercial concentrated ammonium hydroxide according to the method given in the previous example gives the desired ammonium salt of compound I.

EXAMPLE 5 Preparation of the dimethylamine salt of compound I Compound I (0.5 mole) is dissolved in 500 cc. of dry ether and treated with dimethylamine (22.5 g.; 0.5 mole). The solid whichseparates is filtered, washed twice with cc. portions of cold ether, filtered, pressed dry, and dried completely in a vacuum oven to give the desired dimethylamine salt of compound I.

1 Compound I (0.5 mole) is treated with morpholine (43.5 g.; 0.5 mole) in 500 cc. of ether, and the product is worked up as described for the preparation of the dimethylamine salt to give the desired morpholine salt of compound I.

EXAMPLE 8 Compound I (0.5 mole), ethyl alcohol (23 g.; 0.5 mole), and 3.0 g. of p-toluenesulfonic acid are dissolved in 500 ml. of benzene, and the solution is plalced in a 1-liter, round-bottomed flask fitted with a reflux condenser and a calibrated Dean-Stark tube. The solution is heated at reflux temperature until 9 cc. of water have been collected in the Dean-Stark tube. Thecooled reaction mixture is then extracted twice with 50-cc. portions of 10% sodium carbonate solution, and filtered. The benzene is distilled off in vacuo on the steam bath, and the residue is then distilled in vacuo to give the desired ethyl ester of compound 1.

EXAMPLE 9 Preparation of the decyl ester of compound I In the manner and apparatus described in the previous example, compound I (0.5 mole) and normal primary decyl alcohol (79 g.; 0.5 mole) are refluxed in 500 ml. of benzene in the presence of 3.0 g. of p-toluenesulfonic acid until 9 cc. of water have been distilled from the reaction mixture. Work-up of the reaction mixture as described in the previous example gives the desired decyl ester of compound I.

EXAMPLE 10 Preparation of the n-butyl ester of compound I The reaction of compound I (0.5 mole) and n-butyl alcohol (37 g.; 0.5 mole) by the method described above for the preparation of the ethyl ester is used to prepare the n-butyl ester of compound 1.

EXAMPLE 11 Preparation of the acid chloride of compound 1 Compound I (1 mole) is' placed with 500 cc. of dry benzene in a 2-liter, 3-n'ecked, round-bottomed flask fitted with a mechanical stirrer, reflux condenser (calcium chloride tube), and dropping funnel. Phosphorus trichloride (123 g. 0.9 mole) is added slowly dropwise with vigorous stirring while the reaction flask is cooled with cold water if necessary to control the reaction. When all the PCl has been added and the evolution of hydrogen chloride has ceased, the reaction mixture is then transferred to distillation apparatus, and the solvent is distilled ofl. The residue is then distilled in vacuo to give the desired acid chloride of compound I.

EXAMPLE 12 Preparation of the amide of compound I One mole of the acid chloride of compound I is placed with 500 cc. of dry benzene in a l-liter, B-necked flask fitted with a reflux condenser, mechanical stirrer, and a gas inlet tube having a sparger tip. The mixture is stirred while dry ammonia gas is passed into the mixture for several hours. When the ammonia gas is no longer taken up, the precipitated salt is filtered off and extracted twice with 100 ml. portions of ether. The ether extracts and benzene filtrate are dried over magnesium sulfate and filtered, and the solvents are distilled off to give the desired amide of compound I.

EXAMPLE 13 Preparation of the N-n-decylamide of compound 1 6. ether. The ether extracts and benzene filtrate are dried over magnesium sulfate and filtered. Distillation of the solvents gives the desired N-n-decylamide of compound I.

EXAMPLE 14 Preparation of the N,N-diethylamide of compound I One mole of the acid chloride of compound I is treated with diethylamine (146 g.; 2.0 moles) in the manner and apparatus described in the previous example to give the N,N-diethylamide of compound I.

EXAMPLE 15 Preparation of the anhydride 0 compound I Dry pyridinet 158 g.; 2.0 moles) and 1 liter of dry benzene are placed in a 2-liter, S-necked, round-bottom flask fitted with a dropping funnel, mechanical stirrer, reflux condenser, and internal thermometer. One mole of the acid chloride of compound I, which is prepared as described in a previous example, is added rapidly with stirring to the reaction mixture. Compound I (1 mole) is then added in portions over a period of about 10 minutes with rapid stirring. The pyridine hydrochloride which precipitates is filtered oil, and the benzene is distilled from the filtrate in vacuo. The residue contains the desired anhydride of compound I, Which can be purified by crystallization from a suitable solvent.

EXAMPLE 16 Preparation of an emulsifiable concentrate of compound I The following concentrate is prepared by mixing the ingredients intimately in the given percentage proportions by weight:

Percent Compound I 25 Antarox A-400 40 Methanol 35 Antarox A400 is the trade name under which a nonionic detergent of the aromatic polyethylene glycol ether type is sold. The above concentrate is diluted with water to the desired concentration for use.

EXAMPLE 17 Preparation of an emulsifiable concentrate of the n-butyl ester of compound I The following ingredients are mixed thoroughly in the given percentage proportions by Weight:

The above concentrate is diluted with water to the desired concentration for use.

EXAMPLE 18 Preparation of a dust from the sodium salt of compound I The sodium salt of compound I (10% by weight) and talc by weight) are combined and ground to the desired particle size in a mechanical grinder-blender.

The herbicidal activity of chemical compounds is often demonstrated by the ability of the chemicals to kill or arrest the growth of tomato plants. The tomato plant is readily grown and maintained under uniform conditions for experimental purposes in greenhouses, and its response to chemicals is very similar to that observed for a wide variety of economically important species of undesirable plant life in the field.

The herbicidal activity of the compounds of this invention, for example, can be demonstrated in greenhouse experiments on young potted tomato plants (Bonny Best variety). The compounds are formulated into 10 percent wettable powders and are dispersed in water at a concentrationof 2,000 parts per million actual chemical. Ten milliliters of an aliquot portion of the dispersion is added to the soil surface of the tomato plants, approximately to 7 inches tall. In order to avoid undue concentration or accumulation of the chemical in any given area, 5 holes the size of a pencil and about 1 inch deep are punched in the soil surface around the shoot, and the milliliter application is divided equally among the 5 holes. Three plants are used for each application. The treated plants are held under greenhouse conditions for 7 days, provided with subterranean Watering, and observed for response to treatment. The results indicate a high order of herbicidal toxicity of the compounds of this invention.

I claim as my invention:

1. A method of destroying undesirable plants which comprises contacting said plants with a herbicidal composition comprising an inert carrier and as the essential active ingredient, in a quantity which is injurious to said plants, a compound selected from the group consisting of 2,6-dimethoxy-3-chlorobenzoic acid, its esters in which the esterifying group is an unsubstituted alkyl group containing from one toten carbon atoms, its alkali metal and amine salts in which the amine component contains up to ten carbon atoms, its anhydride, and its amides in which the amine component contains up to ten carbon atoms.

2. A method as described in claim 1, wherein the compound is an alkali metal salt of 2,6-dimethoxy-3-chlorm benzoic acid.

3, A method as described in claim 1, wherein the compound is an amine salt of 2,6-dimethoxy-3-chlorobenzoic acid in which the amine component contains up to ten carbon atoms.

4. A method as described in claim 1, wherein the compound is an ester of 2,6-dimethoxy-3-ch1orobenzoic acid in which the esterifyinggroup is an unsubstituted alkyl group containing from one to ten carbon atoms.

5. A method as described in claim 1, wherein the compound is an amide of 2,6-dimethoxy-3-chlorobenzoic acid in which the amine component contains up to ten carbon atoms. 7

6. A method as described in claim 1, wherein the compound is 2,6-dimethoXy-3-chlorobenzoic acid.

7. A method as described in claim 1, wherein the compound is sodium 2,6-dimethoxy-3-chlorobenzoate.

8. A method as described in claim 1, wherein the compound is the diethanolamine salt of 2,6-dimethoxy-3- chlorobenzoic acid.

9. -A method as described in claim. 1, wherein the compound is n-butyl 2,6-dimethoXy-3-chlorobenzoate.

10. A method as described in claim 1, wherein the compound is bis(2,6 dimethoxy 3 chlorobenzoic) anhydride.

References Cited in the file of this patent UNITED STATES PATENTS 2,394,916 Jones Feb. 12, 1946 2,577,969 Jones Dec. 11, 1951 2,843,470 Searle July 15, 1958 OTHER REFERENCES in Chemical Abstracts, vol. 47, 

1. A METHOD OF DESTROYING UNDESIRABLE PLANTS WHICH COMPRISES CONTACTING SAID PLANTS WITH A HERBICIDAL COMPOSITION COMPRISING AN INERT CARRIER AND AS THE ESSENTIAL ACTIVE INGREDIENT, IN A QUANTITY WHICH IS INJURIOUS TO SAID PLANTS, A COMPOUND SELECTED FROM THE GROUP CONSISTING OF 2,6-DIMETHOXY-3-CHLOROBENZOIC ACID, ITS ESTERS IN WHICH THE ESTERIFYING GROUP IS AN UNSUBSTITUTED ALKYL GROUP CONTAINING FROM ONE TO TEN CARBON ATOMS, ITS ALKALI METAL AND AMINE SALTS IN WHICH THE AMINE COMPONENT CONTAINS UP TO TEN CARBON ATOMS, ITS ANHYDRIDE, AND ITS AMIDES IN WHICH THE AMINE COMPONENT CONTAINS UP TO TEN CARBON ATOMS. 